Field of the Disclosure
The subject matter of this application relates generally to biological fluid processing systems and methods such as biological fluid separation systems and methods. More particularly, the subject matter relates to methods, devices and systems for controlling fluid flow and, more particularly, for controlling flow rates and pressures in a fluid flow path such as a return or infusion flow path that may be connected to a human subject.
Description of Related Art
Various blood processing systems now make it possible to collect and/or process particular blood constituents, instead of whole blood, from a blood source such as, but not limited to, a container of previously collected blood or other living or non-living source. Typically, in such systems, whole blood is drawn from a blood source, a particular blood component or constituent is separated, removed, and collected, and the remaining blood constituents are returned to the blood source. Removing only particular constituents is advantageous when the blood source is a human donor, because potentially less time is needed for the donor's body to return to pre-donation levels, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for transfer and/or therapeutic treatment.
Whole blood is typically separated into one or more of its constituents (e.g., red cells, platelets, and plasma) by processing through a disposable fluid flow circuit that is associated with a durable, reusable device that controls the processing of fluid through the flow circuit by a variety of pumps, valves, sensors and the like that operate on the fluid flow circuit. Typical separation techniques include centrifugation, such as in the AMICUS® separator from Fenwal, Inc. of Lake Zurich, Ill., or other centrifugal separation devices, or membrane separation such as a spinning membrane-type separator, such as the AUTOPHERESIS-C® and AURORA® devices from Fenwal, Inc.
While the above refers to apheresis systems in particular, the present subject matter, as seen below, is not limited to such whole blood apheresis applications but may include systems for processing blood components or other biological fluid components. With reference to apheresis systems, as noted above, blood components that are not collected are typically returned to the source or subject, such as a patient or donor. These may include concentrated red cells, plasma, platelets or some combination of these. Also, it is common to infuse into the donor or patient a replacement fluid, such as saline, to replace the volume of the blood components that have been removed and not returned. To this end, such systems include a fluid flow path that communicates with the source or subject, such as but not limited to a human donor or patient, for directing or returning blood, blood components or other fluids to the subject. The fluid flow path is usually in the form of flexible plastic flow tubing terminating in a needle or other access device that is inserted into a subject's (human donor's or patient's) vein.
So as not unduly to extend the time required of a donor or patient in an apheresis procedure, it is beneficial for the flow rate in the return or infusion fluid flow path to be as fast as reasonably possible. However, the flow rate is constrained by several factors. For example, it may be desired not to exceed certain pressure thresholds or limits that may be potentially detrimental or uncomfortable for the subject.
Another complicating factor is fluid flow path occlusions, which may lead to occlusion alarms. Infusion of fluid into a donor or patient sometimes encounters flow blockages or occlusions that may be physiologically related, such as clotting, blood vessel limits or needle position within the subject's vein, or due to equipment related issues such as inadvertently crimped infusion flow tubing, or the like. In prior systems, such occlusions are commonly detected by the processing system from increased fluid pressure within the infusion fluid flow path, and typically resulted in an alarm condition being generated to alert the system operator of the occlusion. This alarm condition was often accompanied by automatic stoppage of the apheresis procedure and/or the infusion fluid flow to the subject. Of course, the requirement for operator intervention to identify and clear the source of the alarm and the temporary interruption in the procedure combine to create potentially increased procedure time and greater burden on the operator, who may be overseeing the operation of several apheresis procedures at the same time. As a result, there is continuing desire to provide apheresis and other similar biological fluid processing systems and methods that will tend to reduce the incidence of unnecessary occlusion alarms while also limiting procedure time delays. The present subject matter relates to such methods, devices and systems.